“…And curve-fitting errors and discontinuous or inaccurate high-order derivatives in current and voltage expressions, always lead to inaccurate predictions of intermodulation distortion (IMD). Different equivalent such as physics-driven modeling, analytical modeling, empirical modeling and equivalent circuit modeling, have been investigated (especially for PIN-PDs), an accurate equivalent circuit model, which accounts for the unique device structure and operation mechanism of UTC-PD with dipole-doped structure is still lacking [24][25][26]. Wu et al [27] proposed an analytical equivalent circuit model for nearballistic UTC-PD.…”